What does the Bible say about the importance of a changed heart?

A changed heart signifies a transformation that occurs through the work of the Holy Spirit, aligning one's desires with God's will. The conversion of the Apostle Paul exemplifies this change, where he shifted from persecuting Christians to preaching the gospel. The doctrine of regeneration teaches that without a new heart, one cannot genuinely desire to follow God or align with His purposes. As stated in John 1:13, we are 'born... of God,' signifying that our change is not of our own doing but a divine act.